HP 86: Strange Error

[Michael Fehlhammer]

My newly acquired HP 86A displays a strange warning immediately after power on:
Warning 27: 85 ROM disabled.
Needless to say that I didn't plug in an HP 85 ROM. I tested without any module plugged in.
I wrote a short BASIC program, so far the machine seems to work fine.
Does anybody has an idea what could be the reason for the strange warning?

[rprosperi]

(11-19-2017 12:07 AM)Michael Fehlhammer Wrote:  My newly acquired HP 86A displays a strange warning immediately after power on:
Warning 27: 85 ROM disabled.

Michael - The HP-87 "Operating and BASIC Programming Manual" (I don't have '86 docs, but as you know they are quite similar) includes Error 27 (a warning) in the Error Message Appendix with this Error Condition note:

"An HP-83/85 ROM is installed in the ROM drawer. The ROM is ignored by the system if no ROM with the same ROM number is present."

The wording of the final sentence is a bit strange to me, as I'm not sure how some other ROM could have the same ROM number as an 83/85 system ROM; perhaps this could happen if some signal lines on a board are damaged?

Any chance there are additional ROMs installed internally?

Assuming it's a false positive, I'd say it's likely safe to ignore as far as how it will affect your use of the machine, since it is disabled. The actual cause of the condition may be reason for concern though as something is being detected incorrectly.

[Paul Berger (Canada)]

(11-19-2017 12:22 AM)rprosperi Wrote:  

(11-19-2017 12:07 AM)Michael Fehlhammer Wrote:  My newly acquired HP 86A displays a strange warning immediately after power on:
Warning 27: 85 ROM disabled.

Michael - The HP-87 "Operating and BASIC Programming Manual" (I don't have '86 docs, but as you know they are quite similar) includes Error 27 (a warning) in the Error Message Appendix with this Error Condition note:

"An HP-83/85 ROM is installed in the ROM drawer. The ROM is ignored by the system if no ROM with the same ROM number is present."

The wording of the final sentence is a bit strange to me, as I'm not sure how some other ROM could have the same ROM number as an 83/85 system ROM; perhaps this could happen if some signal lines on a board are damaged?

Any chance there are additional ROMs installed internally?

Assuming it's a false positive, I'd say it's likely safe to ignore as far as how it will affect your use of the machine, since it is disabled. The actual cause of the condition may be reason for concern though as something is being detected incorrectly.

The "ROM number" it is referring to is the select number the ROM is programmed to respond to. In the series 80 machines ROMs are selected by writing this ROM number to a specific address that all the bank selectable ROMs monitor and when a ROM sees its number come up, it enables itself, and if it is someone else's number the ROM disables. Between the 83/85 and 86/87 machines ROMs with similar function have the same ROM number, for instance the assembler ROM is ROM number 40 on both, and if you had both the 83/85 and 86/87 ROM plugged in at the same time both would respond to the ROM number by turning themselves on and the result would be unpredictable, I would suppose that a defective ROM could cause a similar result, the best way to check would be with a diagnostic ROM as it does a more comprehensive test of the ROMs .

[Michael Fehlhammer]

Thank you for your answers!

Since I have no rom drawer installed ( and receive the warning anyway), I might check - like Bob suggested - if there are additional roms installed internally. But - who should have been so stupid to install the wrong kind of rom module inside the case? Not so likely, isn't it? Hmm.
Although I have no clue about hardware, I am afraid Bob's guess "some signal lines on a board are damaged" seems to be a good explanation for this behaviour, unfortunately.

I have got a second computer of the same kind (86A), which works fine.
I could use it for comparison, if I had an idea what should be compared.

In order to plug in the diagnostics rom, I'd have to transfer it onto my PRM-85.
This should be feasible.
Is there a documentation available how to use the diagnostics rom? Probably I should get the HP 86 service manual?

[Paul Berger (Canada)]

I have never seen a service manual for 86A but as far as running diagnostics you can use the 86B manual found on the MoHPC manual collection. On hpmuseum.net there is also a manual "86A-B_Self-PacedLearningGuide" that is a service training course and has a little bit on running diagnostics. The diagnostic ROM is a take over ROM and it will boot up to a prompt for a single character command for the test you want to run, and if you do not enter anything after a few minutes it continues on to BASIC. The ROM test is "D" for the system ROMs and M for expansion ROMs. The 86A apparently has the Mass Storage and Printer ROMs built in as well as the BASIC ROMs.

[Martin Hepperle]

(11-19-2017 12:07 AM)Michael Fehlhammer Wrote:  My newly acquired HP 86A displays a strange warning immediately after power on:
Warning 27: 85 ROM disabled.
Needless to say that I didn't plug in an HP 85 ROM. I tested without any module plugged in.
I wrote a short BASIC program, so far the machine seems to work fine.
Does anybody has an idea what could be the reason for the strange warning?

Michael,

first I would check which ROMs are visible to the machine. My SYSINVentory program (see groups.io) should list all ROMs found on the machine.

Maybe one of the internal System ROMs has a flaw. You could write a BASIC program to read the content of each system ROM (using a PEEK() BPGM), dump the content to a file and then compare with known good ROM images, e.g. from Everett's Series-80 Simulator or a dump your second machine.
If only the checksum byte in a ROM is wrong: no problem. Otherwise you can identify which BASIC function is affected by comparing the location of the error in the ROM with the source code disassembly.

Martin

[Michael Fehlhammer]

Thank you for these tips, Martin.
Then I have to find time to load your program and do some testing.
But in case I should find out that one system rom is buggy - would there be a chance to replace it? I can burn eproms, but where should I get a suitable rom? ( Apart from finding another HP 86 as a donor).

[Paul Berger (Canada)]

Unfortunately the ROMs used in these machines are not industry standard ROMs, this is why we have things like the PRM-85. The ROMs have address selection logic on the die and in the case of ROMs that are bank selected they have the logic that monitors the bank select address and recognizes its ROM number. The internal ROM like the printer and mass storage ROM fitted in the 86A would be the same as ROM as the one you would plug into a ROM card except that it is in a DIP package instead of being wire bonded to a small circuit board inside a plastic module. Cards like the PRM-85 put all this address selection and bank selection logic into a CPLD so that industry standard ROMs can be used to replace the HP custom ROM. It would be possible to make a single image module like this to replace one of the internal ROMs, however if one of them is defective, it might be just as easy to put the image onto something like a PRM-85. One of the OS ROMs is also bank selected but the remaining 3 are at fixed addresses in the memory map, however due to the unique way address and data transfers take place with the Capricorn processor you could not drop an industry standard ROM in to replace them either.